Universal clamping mechanism

ABSTRACT

A method is provided for processing a lead frame. Generally, a first surface of a lead frame base tape is placed on a first surface of the lead frame. A second surface of the lead frame base tape is placed on a first surface of a porous block. A vacuum is placed on a second surface of the porous block. A device for processing lead frames comprises a porous block with a first side and a second side, and a vacuum system connected to the first side of the porous block. The device may also include devices for attaching chips to the lead frame and wire bonding the chips to the lead frame.

FIELD OF THE INVENTION

[0001] The present invention relates generally to integrated circuitpackages. More specifically, the invention relates to the clamping oflead frames during the manufacturing of a Leadless Leadframe Package.

BACKGROUND OF THE INVENTION

[0002] An integrated circuit (IC) package encapsulates an IC chip (die)in a protective casing and may also provide power and signaldistribution between the IC chip and an external printed circuit board(PCB). An IC package may use a metal lead frame to provide electricalpaths for that distribution. During the process of die attach and wirebonding for conventional semiconductor packages, the semiconductor leadframe or substrate material rests on a base block during the epoxydispensing, die attaching, and wire bonding processes. During theseprocesses the frame or substrate needs to be held down firmly to aheater block by a vacuum, a clamp, or both.

[0003] To facilitate discussion, FIG. 1 is a top view of a lead framepanel 100 made up for a plurality of lead frames that may be used in theprior art. The lead frame may comprise leads 108, die attach pads 112,ties 116 for supporting the die attach pads 112 and leads 108, and askirt 120 for supporting the plurality of leads 108 and ties 116. Thelead frame panel 100 may be etched or stamped from a thin sheet ofmetal. FIG. 2 is a cross sectional view of the lead frame panel 100shown in FIG. 1, along cut lines 2-2, attached to a lead frame base tape204, which is mounted on a base block 208 used in the prior art. Thebase block 208 has a plurality of holes 212, through which a vacuum isapplied to the lead frame base tape 204 to hold the lead frame 100 andthe lead frame base tape 204 to the base block 208. A top clamp 216 mayalso be used to hold the lead frame 100 and lead frame base tape 204 tothe base block 208. Preferably, the holes 212 are positioned at the dieattach pads 112, not between the die attach pads 112 and the ties 116 orat the ties 116. As a result, a base block with a configuration of holesfor one type of lead frame may not be useful in clamping another type oflead frame.

[0004]FIG. 3 is a cross sectional view of another type of lead frame 300mounted on the base block 208 that is used in FIG. 2. Tape 304 is placedacross the leads, die attach pads 312, the ties 308, and skirt 320 ofthe lead frame 300. The tape 304 and lead frame 300 are placed on thebase block 208. Two vacuum holes 212 are under parts of the tape 304connected to die attach pads 312 and two vacuum holes 212 are under tape304 that is next to a gap between a lead 308 and a die attach pad 312.Placing a lead 308 or gap over a vacuum hole 212 may cause the leadframe to float or bounce during the wire bonding process. As a result,the vacuum provided through the base block 208, even in combination witha clamping 316 may not be sufficient to secure the lead frame during thewire bonding and die attach process.

[0005] It is desirable to provide a universal base block that is able tosecure different lead frame configurations.

SUMMARY OF THE INVENTION

[0006] To achieve the foregoing and other objects and in accordance withthe purpose of the present invention, a variety of techniques isprovided for processing a lead frame. Generally, a first surface of alead frame base tape is placed on a first surface of the lead frame. Asecond surface of the lead frame base tape is placed on a first surfaceof a porous block. A vacuum is placed on a second surface of the porousblock.

[0007] Another aspect of the invention provides a device for processinglead frames, comprising a porous block with a first side and a secondside, and a vacuum system connected to the first side of the porousblock.

[0008] These and other features of the present invention will bedescribed in more detail below in the detailed description of theinvention and in conjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention is illustrated by way of example, and notby way of limitation, in the figures of the accompanying drawings and inwhich like reference numerals refer to similar elements and in which:

[0010]FIG. 1 is a plan view of a lead frame and die assembly used in theprior art.

[0011]FIG. 2 is a cross sectional view of the lead frame panel shown inFIG. 1, along cut lines 2-2, attached to a lead frame base tape, whichis mounted on a prior art base block.

[0012]FIG. 3 is a cross sectional view of another type of lead framemounted on the prior art base block that is used in FIG. 2.

[0013]FIG. 4 is a top view of a base block used in a preferredembodiment of the invention.

[0014]FIG. 5 is an enlarged view of part of the frame and porous block,shown in FIG. 4.

[0015]FIG. 6 is a cross-sectional schematic view of the base block beingused in a die attach and wire bonding device.

[0016]FIG. 7 is an enlarged cross-sectional view of part of the baseblock shown in FIG. 6.

[0017]FIG. 8 is an enlarged cross-sectional view of an alternative baseblock in another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The present invention will now be described in detail withreference to a few preferred embodiments thereof as illustrated in theaccompanying drawings. In the following description, numerous specificdetails are set forth in order to provide a thorough understanding ofthe present invention. It will be apparent, however, to one skilled inthe art, that the present invention may be practiced without some or allof these specific details. In other instances, well-known process stepsand/or structures have not been described in detail in order to notunnecessarily obscure the present invention.

[0019] To facilitate discussion, FIG. 4 is a top view of a base block400 used in a preferred embodiment of the invention. The base block 400comprises a frame 404 and a porous block 408 mounted within the frame404. FIG. 5 is an enlarged view of part of the frame 404 and porousblock 408. The porous block 408 is defined as a block with a pluralityof holes 412 on the upper surface of the porous block 408. The holes 412have a diameter in the range of 0.005 mm to 2.00 mm. More preferably,the holes 412 have a diameter in the range of 0.005 mm to 1.50 mm. Mostpreferably, the holes 412 have a diameter in the range of 0.005 mm to0.200 mm. The diameters of the holes 412 are set so that air passingthrough the holes will have a some resistance and yet wide enough toallow a vacuum pressure to be applied through the holes. The density ofthe holes are at least 5 holes per square centimeter. More preferably,the density of holes are at least 10 holes per square centimeter. Mostpreferably, the density of holes are at least 15 holes per squarecentimeter. Preferably, the ratio of the area of the holes to the areaof the remainder of the upper surface of the porous block is at least20%. More preferably, the ratio of the area of the holes to the area ofthe remainder of the upper surface of the porous block is at least 40%.Most preferably, the ratio of the area of the holes to the area of theremainder of the upper surface of the porous block is at least 60%.

[0020]FIG. 6 is a cross-sectional schematic view of the base block 400being used in a die attach and wire bonding device 600. The base block400 is mounted on a vacuum device 604, which uses an exhaust fan 608 tocreate a vacuum across the bottom side of the porous block 408 of thebase block 400. A heater 612 is thermally connected to the base block400, so that the heater 612 may heat the base block to temperatures onthe order of 150° C. A lead frame 620 mounted on lead frame base tape624 is placed on the top surface of the porous block 408 of the baseblock 400. A top clamp 628 may be used to help hold the lead frame 620to the base block 400. In operation, the exhaust fan 608 and vacuumdevice 604 create a vacuum on the bottom surface of the porous block 408of the base block 400. A further definition of the porous block 408 isthat the porous block forms passageways between the holes on the topsurface of the porous block 408 and the bottom surface of the porousblock 408, so that the vacuum applied to the bottom surface of theporous block 408 generates a vacuum at the holes 412 (FIG. 5) at the topsurface of the porous block 408. The vacuum is applied through the holes412 (FIG. 5) to the lead frame base tape 610. Since the holes 412 arespaced to cover at least 60% of the surface of the base block 400, atleast 50% of the lead frame base tape 624 connected to the die attachpad 632 will be held by the vacuum from the holes 412. The base blockmay provide an evenly distributed vacuum across the surface of the leadframe 624, which may provide a better holding without movement than theprior art. In addition, if a different lead frame is used with adifferent die attach pad, lead, and tie pattern the base block 400 wouldbe able to provide an improved hold with the different lead frame. Thisallows the base block 400 to serve as a universal base block, which doesnot need to be changed when the lead frame pattern is changed.

[0021] A chip attaching device 640 is used to attach chips 644 to thedie attach pads 632. The chip attaching device 640 may use an epoxy 648to mechanically connect the chips 644 to the die attach pads 632. Theheater 612 may then heat the base block 400 to about 150° C. A wirebonding device 652 may then be used to create wire bonds 656 between thechips 644 and leads of the lead frame 624. Heating the lead frame 624 toabout 150° C. may help during the wire bonding process.

[0022] The porous block 408 may be formed from any hard porous materialon the market, such as ceramic or stone. However, in the case whereconducting heat from a heater to the lead frame is done through theporous block 408, it is desirable to use a metal porous block. Suchmetal porous blocks may be naturally porous or a plurality of pin holesmay be formed in the metal to form a metal porous block. FIG. 7 is anenlarged cross-sectional view of part of the base block shown in FIG. 6in one embodiment of the invention. The base block 400 comprises theframe 404 and the porous block 408, which is shaded to indicate that thematerial of the porous block 408 is porous. FIG. 8 is an enlargedcross-sectional view of an alternative base block 800, which comprises aframe 804 and a porous block 808, which in this case is a solid blockwith a plurality of pin holes 812 that have placed through the porousblock 808. The pin holes 812 may be formed using lasers or mechanicaldrills or by other methods. The pin holes may be in a uniform pattern orrandomly distributed, as long as the pin holes are within the diameterrange, density range, and area ratio range as described above. The pinholes or porousness allow the holes to be in fluid contact with thevacuum device 604.

[0023] In an alternative embodiment, especially if straight through pinholes are used, the base block may be made without a frame or the framemay be formed by outer walls of outer pin holes.

[0024] While this invention has been described in terms of severalpreferred embodiments, there are alterations, modifications,permutations, and substitute equivalents, which fall within the scope ofthis invention. It should also be noted that there are many alternativeways of implementing the methods and apparatuses of the presentinvention. It is therefore intended that the following appended claimsbe interpreted as including all such alterations, permutations, andsubstitute equivalents as fall within the true spirit and scope of thepresent invention.

What is claimed is:
 1. A device for processing lead frames, comprising:a porous block with a first side and a second side; and a vacuum systemconnected to the first side of the porous block.
 2. The device, asrecited in claim 2, wherein the porous block comprises a plurality ofholes on the second side of the porous block wherein the diameter ofeach of the plurality of holes is less than 2.00 mm and wherein theplurality of holes are in fluid connection with the vacuum system. 3.The device, as recited in claim 2, further comprising a chip attachingdevice on the second side of the porous block.
 4. The device, as recitedin claim 3, further comprising a wire bonding device on the second sideof the porous block.
 5. The device, as recited in claim 4, furthercomprising a heater connected to the first side of the porous block. 6.The device, as recited in claim 5, wherein a density of the plurality ofholes is at least 5 holes per square centimeter.
 7. The device, asrecited in claim 6, wherein the plurality of holes have an area and thesecond side of the porous block has an area wherein the area of theholes and the area of the second side of the porous block have a ratio,wherein the ratio of the area of the holes to the area of the secondside of the porous block is at least 20%.
 8. The device, as recited inclaim 7, further comprising a clamp for clamping a lead frame to thesecond side of the porous block.
 9. The device, as recited in claim 1,further comprising a clamp for clamping a lead frame to the second sideof the porous block.
 10. The device, as recited in claim 9, wherein theporous block comprises a plurality of holes on the second side of theporous block wherein the diameter of each of the plurality of holes isbetween 0.005 mm to 0.200 mm.
 11. A method for processing a lead frame,comprising: placing a first surface of a lead frame base tape on a firstsurface of the lead frame; placing a second surface of the lead framebase tape on a first surface of a porous block; and applying a vacuum ona second surface of the porous block, which causes a vacuum to beapplied to the second surface of the lead frame base tape.
 12. Themethod, as recited in claim 11, wherein to porous block comprises aplurality of holes on the second side of the porous block, wherein thediameter of each of the plurality of holes is less than 2.00 mm andwherein the vacuum is applied to the second surface of the lead framebase tape through the plurality of holes.
 13. The method, as recited inclaim 12, further comprising applying chips to a second surface of thelead frame.
 14. The method, as recited in claim 13, further comprisingheating the porous block.
 15. The method, as recited in claim 14,further comprising providing wire bonding between the lead frame and thechips.
 16. The method, as recited in claim 15, wherein a density of theplurality of holes is at least 5 holes per square centimeter.
 17. Themethod, as recited in claim 16, wherein the plurality of holes have anarea and the second side of the porous block has an area wherein thearea of the holes and the area of the second side of the porous blockhave a ratio, wherein the ratio of the area of the holes to the area ofthe second side of the porous block is at least 20%.
 18. The method, asrecited in claim 17, further comprising clamping the lead frame to thesecond side of the porous block
 19. A device for processing lead frames,comprising: a porous block with a first side and a second side, whereinthe porous block comprises a plurality of holes on the second side ofthe porous block, wherein the diameter of each of the plurality of holesis in the range of 0.005 mm to 2.00 mm; a vacuum system connected to thefirst side of the porous block, wherein the plurality of holes on thesecond side of the porous block are in fluid connection with the vacuumsystem; a heater connected to the first side of the porous block; and achip attaching device on the second side of the porous block.